This invention relates to apparatus and methods for broadcasting and receiving data, including digital television signals, voice signals, and other data. More particularly, this invention relates to an apparatus and method for providing terrestrial transmissions simultaneously along with direct broadcast satellite transmissions on a common frequency.
Currently, television signals may be received from a satellite in geosynchronous orbit about the earth. The television signals are transmitted from a terrestrial transmitter to the satellite, perhaps communicated between different satellites, and then retransmitted from a satellite so that the signals can be received by terrestrial receivers within a certain geographic receiving area within a line of sight of the satellite. In addition to television signals, other types of data may also be transmitted to consumers through satellites in either geosynchronous or non-geosynchronous orbit.
Direct broadcast satellite service (DBS) refers to satellite transmission of television signals and other data directly for use by individual households or subscribers having the proper signal receiving equipment. The U.S. Federal Communications Commission has dedicated the electromagnetic spectrum from 12.2 gigahertz to 12.7 gigahertz for DBS broadcasting. Numerous signal carriers are located within the DBS spectrum, each carrier carrying several individual television channels. Depending upon the compression technology applied to these signals, literally hundreds of separate channels may be available through DBS. A great benefit of the DBS system as opposed to prior satellite systems is that only a small dish-type antenna is required to receive the DBS signals and the alignment of the receiving dish is not as critical as earlier satellite broadcast systems. Also, the DBS system will provide high quality reception at any point in the geographic receiving area of a satellite without the expense of land transmission lines such as those required for cable television.
Current regulations require that DBS satellites be separated from each other by at least nine (9) degrees in a geosynchronous arc. The receiving antenna for DBS signals must, therefore, be limited to receiving signals in a directional range measuring plus or minus nine (9) degrees from a centerline of the antenna. Receiving signals in a range wider than the satellite spacing would cause interference by signals transmitted by different satellites on the same frequency. The limited directional reception range of the DBS receiving antenna is the result of the gain provided by the antenna being asymmetrical about the antenna structure. DBS signals reaching the DBS receiving antenna at angles outside of the directional range of the antenna receive insufficient gain to interfere with the desired DBS signals received within the antenna directional range.
U.S. Pat. No. 5,483,663 is directed to a system having a receiver arrangement in which DBS and terrestrial signals are received within similar frequency bands. The system shown in the U.S. Pat. No. 5,483,663 may be implemented with a multiple antenna arrangement, or with a single, moveable antenna. In the multiple antenna arrangement, two separate antennas direct the received signals to a common propagation path for processing as if they were received by a single antenna and transmitted from a single location. In the single antenna arrangement, the antenna is movable between a position to receive DBS signals and another position to receive terrestrial signals.
The advantage of the system shown in U.S. Pat. No. 5,483,663 is that local originating signals, whether carrying data for television or other data, may be received simultaneously with DBS signals, and processed with the same or similar equipment as that used to process the DBS signals. The local originating signals may carry local television programming which may be received along with the national or regional DBS television programming.
It is an object of the invention to provide terrestrially transmitted signals simultaneously with satellite transmitted signals at the same frequency. The invention includes an apparatus and method for transmitting terrestrial signals simultaneously with satellite signals transmitted at a common frequency.
The object of the invention is accomplished by transmitting terrestrial signals in a manner which ensures that they do not interfere with satellite signals transmitted at the same frequency. Embodiments of the invention may take advantage of receiving antennae having a limited directional reception range or satellite receiving window and may include transmitting the terrestrial signals in a different range of directions than those in which the satellite signals are transmitted. The power level at which the terrestrial signals are transmitted and the directional nature of the satellite receiving antennae ensure that the satellite transmitted signals can be discriminated from the terrestrially transmitted signals. Although the terrestrial signal transmission power is limited to a non-interfering transmission power level, the terrestrial transmission is still strong enough to produce a usable signal at a distant location.
Several different signals will be discussed in this disclosure. The term xe2x80x9csatellite signalsxe2x80x9d refers to signals transmitted directly from a satellite, whereas the term xe2x80x9cterrestrial signalsxe2x80x9d refers to signals transmitted directly from a terrestrial transmitter. xe2x80x9cSatellite input signalsxe2x80x9d refers to signals resulting from satellite signals which have been picked up by an antenna and subjected to gain provided by the antenna. Finally, xe2x80x9cterrestrial input signalsxe2x80x9d refers to signals resulting from terrestrial signals which have been picked up by an antenna and subjected to gain provided by the antenna.
The invention is employed in the situation in which satellite signals are transmitted at a satellite transmission frequency to a terrestrial location. The satellite signals travel along a satellite signal route from the satellite to the terrestrial location and to a satellite receiving antenna at the location for receiving the satellite signals. In some embodiments of the invention, the satellite receiving antenna is omni-directional, that is, provides generally the same gain regardless of the direction from which the signals reach the antenna. In other forms of the invention, the satellite receiving antenna has a directional reception characteristic in which the antenna provides higher gain for satellite signals received within an antenna look angle or satellite receiving window.
The omni-directional satellite receiving antenna need not be oriented in a particular direction to receive signals from a satellite. However, in order to receive satellite signals with the directional satellite receiving antenna, the antenna must be aligned in a satellite reception position. In this satellite reception position, the satellite signal route lies within the satellite receiving window and the satellite signals receive sufficient gain from the antenna structure to produce satellite input signals which are at least at a usable input signal level. This minimum usable input signal level represents the minimum input signal level at which the receiving or signal processing equipment can extract the desired data.
According to the invention, the terrestrial signals are transmitted at the same frequency as the satellite signals. The terrestrial signals are transmitted along a wireless route from the terrestrial transmitter to a user location which may have a satellite receiving antenna. The invention avoids interference between the terrestrial and satellite signals by ensuring that the power level of the terrestrial input signals at the satellite receiving antenna is below an interference level with respect to the satellite input signals at the satellite receiving antenna. The interference level is an input signal power level which is so close in power to the satellite input signal power level that the satellite input signals cannot be discriminated or distinguished. Terrestrial input signals below the interference level do not prevent the receiving or signal processing equipment associated with the satellite receiving antenna from distinguishing and extracting data from the satellite input signals. Also according to the invention, although the terrestrial signals are transmitted so that they do not interfere with the satellite signals, the terrestrial signals present at the user location must be strong enough so that they may be received by an appropriately aligned terrestrial receiving antenna at the location, and distinguished from satellite input signals at the terrestrial receiving antenna. That is, the terrestrial signals present at the location must be at least at a minimum usable terrestrial signal level.
Where the satellite receiving antenna is omni-directional, both the satellite signals and the terrestrial signals picked up by the antenna receive substantially the same gain. Thus, for omni-directional satellite receiving antennae, the terrestrial transmission power level must be controlled so that the terrestrial signals present at the user location have a sufficiently lower power level than the satellite signals present at the user location.
Where the satellite receiving antenna at the user location is a directional antenna, the invention may take advantage of the directional characteristic of the antenna and may transmit terrestrial signals at a high enough power level while still producing a terrestrial input signal at the satellite receiving antenna which is below the interference level. In the case of the directional satellite receiving antenna, the antenna is oriented in the satellite reception position at the user location. The terrestrial transmitter is located with respect to the user location such that the wireless transmission route from the terrestrial transmitter to the user location is at a relatively large angle from the satellite signal route to the antenna and outside of the satellite signal receiving window. At this relatively large angle, the terrestrial signals receive much less gain than the satellite signals. Thus, the terrestrial signal power level at the user location may be the same as or even higher than the satellite signal level and, due to the different gain applied to the signals by the antenna structure, still result in a terrestrial input signal having a power level below the interference level with respect to the satellite input signal level.
In some applications of the invention, depending upon the direction at which a directional satellite receiving antenna must be directed to receive satellite signals, the terrestrial transmissions may be limited to a certain azimuth range. This terrestrial transmission azimuth range is limited so that it does not include any directions that are within the satellite reception look angle or satellite receiving window of a directional satellite receiving antenna aligned to receive signals from a particular satellite. In order to cover a large geographic service area for terrestrial signal reception while maintaining the terrestrial transmission power at a non-interfering level, a plurality of terrestrial transmitters may be spaced apart over the area. In this case the effective transmission areas of the different transmitters combine to ensure the terrestrial signals may be received clearly at each location within the desired geographic service area.
The satellite transmissions and terrestrial transmissions may contain or carry any type of data including television, internet communications, voice, video, or any other type of data. Although the invention is not limited to any particular transmission frequencies, the invention is particularly well adapted for transmission frequencies above one thousand (1000) megahertz. Also, although the invention is not limited for use with a particular transmission modulation technique, modulation techniques such as phase modulation and spectrum spreading (frequency hopping) are currently preferred.
These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings. dr
FIG. 1 is a schematic representation showing the positions of a plurality of satellites in relation to a single terrestrial transmitter and a receiver or user location.
FIG. 2 is a somewhat schematic representation of a receiving antenna structure for receiving satellite and terrestrial transmitted signals at a common frequency.
FIG. 3 is a schematic representation of the spacing for a number of terrestrial transmitters required to allow reception over a large geographic area.
FIG. 4 is a schematic representation of a terrestrial transmitter and terrestrial transmission power control arrangement embodying the principles of the invention.